Sulfur containing organosilicon compounds are useful as reactive coupling agents between rubber and silica fillers providing for improved physical properties. They are also useful as adhesion primers for glass, metals and other substrates.
U.S. Pat. Nos. 3,842,111, 3,873,489 and 3,978,103 disclose the preparation of various sulfur containing organosilicon compounds. These organosilicon compounds are prepared by reacting (1) 2 moles of a compound of the formul a EQU Z-Alk-hal
where hal is a chlorine, bromine or iodine; Z is ##STR2## where R.sup.1 is an alkyl of 1 to 4 carbon atoms or phenyl and R.sup.2 is alkoxy of 1 to 8 carbon atoms, cycloalkoxy of 5 to 8 carbon atoms or alkylmercapto with 1 to 8 carbon atoms; Alk is a divalent aliphatic hydrocarbon or unsaturated hydrocarbon or a cyclic hydrocarbon containing 1 to 18 carbon atoms; with (2) 1 mole of a compound of the formula EQU Me.sub.2 S.sub.n
where Me is ammonium or a metal atom and n is a whole number from 2 to 6. Since the two starting materials are liquid, the reaction can take place in the absence of a solvent; however, a volatile inert organic solvent is not only generally used but is preferred. The reaction is carried out with the exclusion of water. The reason for the exclusion of water is to avoid the alkaline hydrolysis reaction of the silyl alkoxy groups which will ultimately lead to insoluble polymeric by-products and lower the overall yield of desired product. Representative organic solvents include aliphatic alcohols such as methyl alcohol and ethyl alcohol. At the end of the reaction between the two starting materials, the separated salt is removed by filtration. The filtrate is then freed from the solvent by distillation under vacuum. Unfortunately, this process suffers from many practical problems. Many of these problems relate to the solvent, e.g. ethyl alcohol. Ethyl alcohol has a low flash point. In addition, it is difficult to obtain and maintain in the water-free (anhydrous) state.